LABORATORY STUDY OF CANNIBALISM AND INTERSPECIFIC PREDATION IN LADYBIRDS

1. In the absence of aphids, adult females of Adalia bipunctata (L.) showed a greater reluctance to eat eggs than males. 2. Eggs and young larvae were more vulnerable to cannibalism than older larvae and starved larvae were more vulnerable than well-fed larvae. 3. Both egg and larval cannibalism is inversely related to the abundance of aphids. 4. Eggs are a better food, in terms of larval growth and survival, than aphids. 5. In the absence of aphids interspecific predation occurred, but not equally, between the coccinellids A.bipunctata, A.decempunctata (L.), Coccinella septempunctata L. and C.undecempunctata L. 6. Larvae and adults of A. bipunctata and C.septempunctata were reluctant to eat conspecific eggs painted with a water extract of the other species' eggs and larvae of C.septempunctata were more likely to die after eating a few eggs of A.bipunctata than vice versa. 7. These results indicate that cannibalism occurs mainly when aphid prey is scarce and is adaptive in that it improves the chances of survival, and coccinellids, to varying degrees, are defended against interspecific predation.